I don't know if it's willful ignorance or what, but most people can't grok the fact that children do not develop in a vacuum. They are in most cases a reflection of their parents' traits and values. Worse for SBF, it is entirely plausible that they had a direct hand in enabling his fraudulent behavior. They were politically-connected Stanford lawyers. It would be foolish to dismiss the possibility of them opening doors and providing cover for their son.
Perhaps an extreme comparison, but I feel the same exact way about adolescent school shooters. We are so quick to absolve and sanctify the parents as if their child's violent tendencies emerged suddenly and spontaneously.